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Bash Redirections Cheat Sheet

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Bash Redirections Cheat Sheet Bash Redirections Cheat Sheet Redirection Description cmd > file Redirect the standard output (stdout) of cmd to a file. cmd 1> file Same as cmd > file. 1 is the default file descriptor (fd) for stdout. cmd 2> file Redirect the standard error (stderr) of cmd to a file. 2 is the default fd for stderr. cmd >> file Append stdout of cmd to a file. cmd 2>> file Append stderr of cmd to a file. cmd &> file Redirect stdout and stderr of cmd to a file. Another way to redirect both stdout and stderr of cmd to a file. This is not the same cmd > file 2>&1 as cmd 2>&1 > file. Redirection order matters! cmd > /dev/null Discard stdout of cmd. cmd 2> /dev/null Discard stderr of cmd. cmd &> /dev/null Discard stdout and stderr of cmd. cmd < file Redirect the contents of the file to the standard input (stdin) of cmd. cmd << EOL line1 Redirect a bunch of lines to the stdin. If 'EOL' is quoted, text is treated literally. This line2 is called a here-document. EOL cmd <<- EOL <tab>foo Redirect a bunch of lines to the stdin and strip the leading tabs. <tab><tab>bar EOL cmd <<< "string" Redirect a single line of text to the stdin of cmd. This is called a here-string. exec 2> file Redirect stderr of all commands to a file forever. exec 3< file Open a file for reading using a custom file descriptor. exec 3> file Open a file for writing using a custom file descriptor. exec 3<> file Open a file for reading and writing using a custom file descriptor. exec 3>&- Close a file descriptor. exec 4>&3 Make file descriptor 4 to be a copy of file descriptor 3. (Copy fd 3 to 4.) exec 4>&3- Copy file descriptor 3 to 4 and close file descriptor 3. echo "foo" >&3 Write to a custom file descriptor. cat <&3 Read from a custom file descriptor. (cmd1; cmd2) > file Redirect stdout from multiple commands to a file (using a sub-shell). { cmd1; cmd2; } > file Redirect stdout from multiple commands to a file (faster; not using a sub-shell). exec 3<> /dev/tcp/host/port Open a TCP connection to host:port. (This is a bash feature, not Linux feature). exec 3<> /dev/udp/host/port Open a UDP connection to host:port. (This is a bash feature, not Linux feature). Redirect stdout of cmd1 to an anonymous fifo, then pass the fifo to cmd as an argument. cmd <(cmd1) Useful when cmd doesn't read from stdin directly. Redirect stdout of cmd1 to an anonymous fifo, then redirect the fifo to stdin of cmd. cmd < <(cmd1) Best example: diff <(find /path1 | sort) <(find /path2 | sort). Redirect stdout of cmd1 and cmd2 to two anonymous fifos, then pass both fifos as cmd <(cmd1) <(cmd2) arguments to cmd. Run cmd2 with its stdin connected to an anonymous fifo, and pass the filename of the cmd1 >(cmd2) pipe as an argument to cmd1. Run cmd2 with its stdin connected to an anonymous fifo, then redirect stdout of cmd cmd1 > >(cmd2) to this anonymous pipe. Redirect stdout of cmd1 to stdin of cmd2. Pro-tip: This is the same as cmd1 > >(cmd2), cmd1 | cmd2 same as cmd2 < <(cmd1), same as > >(cmd2) cmd1, same as < <(cmd1) cmd2. Redirect stdout and stderr of cmd1 to stdin of cmd2 (bash 4.0+ only). Use cmd1 |& cmd2 cmd1 2>&1 | cmd2 for older bashes. cmd | tee file Redirect stdout of cmd to a file and print it to screen. exec {filew}> file Open a file for writing using a named file descriptor called {filew} (bash 4.1+). cmd 3>&1 1>&2 2>&3 Swap stdout and stderr of cmd. cmd > >(cmd1) 2> >(cmd2) Send stdout of cmd to cmd1 and stderr of cmd to cmd2. cmd1 | cmd2 | cmd3 | cmd4 Find out the exit codes of all piped commands. echo ${PIPESTATUS[@]} I explained each one of these redirections in my article All About Bash Redirections: www.catonmat.net/blog/bash-one-liners-explained-part-three/ Did I miss any redirections? Let me know! Email me [email protected], or fork this cheat sheet on github: www.github.com/pkrumins/bash-redirections-cheat-sheet A cheat sheet by Peter Krumins ([email protected], @pkrumins on twitter) www.catonmat.net { good coders code, great coders reuse Released under GNU Free Document License..
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